1. Field of the Invention
The present invention relates to a single-bearing permanent-magnet motor and a single-bearing fan motor.
2. Description of the Related Art
FIG. 4 is a sectional view of a half portion showing a prior-art electronic component refrigerator in which a fan motor 102 using a permanent-magnet motor 101 as a driving source is combined with a heat sink 103 for refrigerating electronic components such as a CPU and which is cut in half at a rotary shaft 103 of the motor 101 as a center. Because there are many patents such as U.S. Pat. No. 5,559,674 which disclose this type of electronic component refrigerator, detailed description will be omitted. In this prior-art fan motor 102, the rotary shaft 103 is supported by two bearings 104 and 105 which are spaced and disposed in an axial direction. This is because large vibration is generated in the axial direction or a vibration phenomenon in which an axis of the rotary shaft swings about a shaft center line at rest occurs when the rotary shaft rotates if only one bearing is provided.
As electronic equipment within which the electronic components are mounted is slimmed down, a desire to slim down the electronic component refrigerator for which this type of fan motor is used is growing. Demands for weight reduction and cost reduction are also intense. In order to satisfy these demands, provision of a single bearing was contemplated, but was not realized in actuality because of the above-described problem.
It is an object of the present invention to provide a single-bearing permanent-magnet motor and a single-bearing fan motor which can suppress generation of vibration or a vibration phenomenon in a rotary shaft even if the rotary shaft is supported by a single bearing.
It is another object of the present invention to provide a single-bearing permanent-magnet motor and a single-bearing fan motor which can suppress vibration in an axial direction of the rotary shaft by a simple structure.
A single-bearing permanent-magnet motor according to the present invention comprises, in a case of an inner rotor-type motor, a rotary shaft, a single bearing for rotatably supporting the rotary shaft, a coming off preventing member mounted to one end of the rotary shaft for preventing the rotary shaft from coming off the bearing, a cup member having a base wall portion fixed to the other end of the rotary shaft and a cylindrical peripheral wall portion standing toward one side in an axial direction of the rotary shaft from an outer peripheral portion of the base wall portion, a permanent magnet unit fixed to an inner peripheral face of the peripheral wall portion such that a plurality of rotor-side magnetic poles formed of permanent magnets are arranged in a peripheral direction of the peripheral wall portion, a motor support having a cylindrical bearing holder that holds the bearing therein, a stator core fixed to the motor support and having a plurality of stator-side magnetic poles each including a pole face disposed to face the respective rotor magnetic poles of the permanent magnet unit, and a plurality of exciting windings mounted to the stator core. In a case of an outer rotor-type motor, the permanent magnet unit is not mounted to the above cup member but positioned on an outside of the bearing holder and fixed to the rotary shaft. The stator core has a plurality of stator-side magnetic poles facing the permanent magnet unit at an inner peripheral portion and is fixed to the motor support.
In the invention, a center (magnetic center in a width direction of the permanent magnet unit) of a width in a direction parallel with the axial direction of the permanent magnet unit is deviating toward the one end side of the rotary shaft from a center (magnetic center in a width direction of the stator-side magnetic poles) of a width in the direction parallel with the axial direction of the pole face of the stator-side magnetic poles. Thus, thrust formed of magnetic attracting force for aligning the magnetic center of the permanent magnet unit in the width direction with the magnetic center of the stator-side magnetic poles in a width direction (thrust toward the other side in the axial direction of the rotary shaft, i.e., thrust from the one end side of the rotary shaft toward the other end side) acts on the rotary shaft. As a result, the coming off preventing member is kept being pushed against the bearing, vibration and swinging of the rotary shaft in the axial direction are suppressed, and the rotary shaft can be supported by the single bearing without a hindrance.
In order to prevent reduction of running torque of the motor, a width dimension in the direction parallel with the axial direction of the rotor-side magnetic poles of the permanent magnet unit is set to be larger than a width dimension in the direction parallel with the axial direction of the stator-side magnetic poles. The permanent magnet unit is fixed to an inner peripheral face of the peripheral wall portion of the cup member such that an end portion of the rotary shaft positioned on the one side in the axial direction projects further than an end portion of a stator core unit positioned on the one side in the axial direction. Thus, it is possible to generate the above thrust and to maintain the running torque similar to that in prior art.
As the bearing to be used, a ball-and-roller bearing or a rolling bearing having a structure in which a plurality of rolling elements such as balls or rollers are disposed between an inner ring and an outer ring is preferable. A projecting dimension of the portion of the rotor-side magnetic poles projecting toward the one side in the axial direction of the rotary shaft is set such that thrust for pushing the coming off preventing member against the inner ring of the rolling bearing has such a value as to sufficiently suppress vibration of the rotary shaft in the axial direction. In the case of the rolling bearing, large friction is not generated between the coming off preventing member and the bearing.
In the case of employing the above structure, if an annular spacer ring is fitted with the rotary shaft such that the spacer ring is positioned between the inner ring of the rolling bearing and the base wall portion of the cup member, the vibration of the rotary shaft in the axial direction can be suppressed even when the thrust is small.
When the respective exciting windings are mounted to the stator core through an insulator made of insulating material, a projecting portion extending further than an end portion of the bearing holder on the cup member side (end portion on the other side in the axial direction of the rotary shaft) may be provided to the insulator. Thus, the projecting portion functions as spacer means to suppress the vibration of the rotary shaft in the axial direction even when the thrust is small if the above spacer ring is not disposed.
If the invention is concretely specified as a single-bearing fan motor, the single-bearing fan motor comprises a rotary shaft, a single rolling bearing for rotatably supporting the rotary shaft, a coming off preventing member mounted to one end of the rotary shaft for preventing the rotary shaft from coming off the rolling bearing, a cup member having a base wall portion fixed to the other end of the rotary shaft and a cylindrical peripheral wall portion standing toward one side in an axial direction of the rotary shaft from an outer peripheral portion of the base wall portion, a permanent magnet unit fixed to an inner peripheral face of the peripheral wall portion such that a plurality of rotor-side magnetic poles formed of permanent magnets are arranged in a peripheral direction of the peripheral wall portion, a plurality of blades fixed to an outer periphery of the peripheral wall portion of the cup member for exhaling toward the other side, a motor support having a cylindrical bearing holder that holds the rolling bearing therein, and a stator core fixed to the motor support and having a plurality of stator-side magnetic poles facing the plurality of rotor-side magnetic poles of the permanent magnet unit. A width dimension in a direction parallel with the axial direction of the rotor-side magnetic poles of the permanent magnet unit is determined such that the rotor-side magnetic poles completely face the stator-side magnetic poles and project toward the one side in the axial direction further than an end portion of the stator-side magnetic poles on the one side in the axial direction and that thrust for pushing the coming off preventing member against an inner ring of the rolling bearing is such a value as to sufficiently suppress vibration of the rotary shaft.
In such a fan motor, it is necessary to generate thrust force that can resist force acting on the rotary shaft by exhalation if a direction of exhalation of the plurality of blades is the same as a direction in which the thrust force acts.